Tubular heater for closed-cycle gas turbine plant



Jan. 4,1966 P.SEIFERT 3, 7,

TUBULAR HEATER FOR CLOSED-CYCLE GAS TURBINE PLANT Filed April 15, 1964 2 Sheets-Sheet 1 11 12 Q f1 8 F M.

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INVENTOR PETE/2 S/FERT BY /JW ATTORNEYS Jan. 4, 1966 P. SEIFERT 3,227,151

TUBULAR HEATER FOR CLOSED-CYCLE GAS TURBINE PLANT Filed April 15, 1964 2 Sheets-Sheet 2 l N VE N TO R Perm SE/FEET ATTORNEYS United States Patent 3,227,151 TUBULAR HEATER FOR CLOSED-CYCLE GAS TURBINE PLANT Peter Seifert, Spreiteubach, Aargau, Switzerland, assignor to Escher Wyss Aktiengesellschaft, Zurich, Switzerland, a corporation of Switzerland Filed Apr. 13, 1964, Ser. No. 359,022 Claims priority, application Switzerland, May 1, 1963,

5,481/ 63 1 3 Claims. (Cl. 126-109) This invention relates to cycle gas turbine plant.

As is known, the working medium of a close-cycle gas turbine plant is heated as high as possible, temperatures of above 500 C. being reached as a rule. Plain steel is resistant to scaling onlyat temperatures of up to 500 C. The tube system, on which the furnace gases impingeis therefore made of heat-resistant, austenitic alloy steels, which are resistant to scaling up to about 1300 C. As is known, resistance to scaling is due to the fact that at high temperatures, there is formed on parts made of austenitic material a dense, firmly adherent oxide film, which protects the underlying material from further oxidation. As is known, the condition for such protection is that the oxide film should actually be formed, and that once formed, the oxide film should persist. This is not the case when the furnace gases contain constituents having an unfavourable influence on the surface of parts made of austenitic material on which the furnace gases impinge and which is to be protected by an oxide film, or

having an unfavourable influence on the oxide film formed on said surface.

When heater units are operated in the said temperature ranges, therefore, either fuel must be burned which in its turn contains no constituents, the presence of which could result in corrosion-producing constituents of the furnace gases, or else it is necessary to ensure that, despite the presence of such constituents in the fuel, after the combustion of the latter, the furnace gases impinging on the heater tubes contain no constituents which could result in corrosion of the tubes.

Processes are known for preventing the harmful effect of fuel constituents. Thus, by adding substances to the fuel or to the combustion products in the immediate vicinity of the place Where the combustion gases are produced, it is possible to prevent the formation of aggressive constituents in the furnace gases or their deposition on the metal parts to be protected.

Fuel free from harmful constituents are expensive and are available in limited amounts only. Their supply is an additional factor of expenditure and is also, for example in the case of ships, a problem of space. Similar considerations apply to the substance to be added to the fuel or combustion gases, and the expenditure involved in adding these substances must also be taken into consideration. Corrosion of the type referred to occurs in accordance with the temperature level existing at a given point of the heater-tube system. In conventional heater units, the steps described for preventing corrosion are adapted to the maximum temperatures prevailing in the heater-tube system. In other words, the combustion gases produced and impinging on the heater tubes correspond to the re quirements of the points of maximum temperature in the heater-tube system, these expensive gases being also admitted to zones of lower temperature, which could admit of combustion gases produced at lower costs without being corroded. An expenditure on fuel or added substances is therefore incurred, Which at least partly remains ineffective or is unnecessary.

This ineffective or unnecessary expenditure is now obviated according to the invention in that, in a tube heater a tubular heater fora closedunit of the kind hereinbefore described, the tube system carrying the working medium and on which the furnace gases impinge, is subdivided into at least two stages, and to at least one stage of higher temperature, combustion gases are admitted which do not contain any constituents giving cause to corrosion of the tubes carrying the Working medium, while to the stage of lower temperature, combustion gases are admitted, which at this low temperature do not give rise to corrosion of the tubes carrying the working medium, but could well produce corrosion in the stage of higher temperature.

constructional examples of the subject of the invention are illustrated in simplified form in the drawing,

wherein:

FIG. 1 shows a diagrammatic section of a two-stage heaterunit with pre-stage,

FIG. 2 shows a diagrammatic section through another constructional form of such a unit, and

FIG. 3 shows a diagrammatic section through yet another constructional form without pre-stage.

The heater unit shown in FIG. 1 has walls 1, 2, 3, 4, 5, 6, confining acombustion chamber 7 of a first heater stage, a combustion chamber 8 of a second heater stage and a pre-chamber 9 of a pre-stage. Heater tubes 10 pass through the pre-chamber and combustion chambers. In the upper wall 3 are two orifices, each of which opens into one of the combustion chambers 7, 8, and which accommodate the burners 11, 12, associated with the combustion chambers. The two arrows V, Z indicate the direction of flow of the waste combustion gases from the combustion chambers 7, 8 into the pre-chamber 9.

The heater tubes 10 enter the pre-chamber 9, pass along its outer wall, and after a double bend at the bottom Wall 2, along the Wall 5, and shortly before encountering .the top wall 3, through the Wall 5 in the vicinity of the burner 11. Here the heater tubes divide into two lines. One line runs along the wall 5 to the bottom wall 2, along the latter to the wall 4 and then along the latter to the vicinity of the burner 12. The other line passes parallel to the top wall 3 to wall 6, along the latter to its lower end, round the short horizontal guide piece of wall 6 to the other side of wall 6 upward to the vicinity of burner 12 and then parallel to Wall 3 to Wall 4, where the two heater tube lines rejoin each other, and then leave the heater through the wall 4.

The working medium flowing in the heater tubes is pre-heated in the pre-chamber 9 of the pre-stage, is thereupon raised to moderate temperature in the combustion chamber 7 of the first heater stage and is then heated to maximum temperature in the combustion chame bet 8 of the second heater stage. Since the local tem; perature of the working medium determines that of the heater tube walls and of the external surfaces of the tubes on which the combustion gases impinge, the tubes of the first stage are less susceptible to corrosion than those of the second stage. The combustion gases impinging on the tubes of the first stage, therefore, in accordance with the maximum temperature occurring in the first stage, may contain more or less constituents, which could give rise to corrosion at the higher temperatures of the second stage, since at the low temperatures occurring in the first stage, the said constituents are incapable of producing corrosion. Only the combustion gases impinging on the tubes of the second heater stage must be adapted to the maximum temperatures occurring in the entire heater unit, that is to say, they must be free from constituents which could give rise to corrosion of the heater tubes.

In the heater unit shown in FIG. 1, each of the two stages with its own combustion chamber 7 and 8, re-

spectively, has its own burner 11 or 12, respectively. It

is thus possible to produce in each combustion chamber combustion gases adapted to the maximum temperature occurring in the corresponding heater-tube system section.

By the steps according to the invention, therefore, it is possible to avoid to a considerable extent a partly ineffective and unnecessary expenditure on high-grade fuel, or substances to be added to the fuel or combustion products, and this expenditure is limited to the amount which is necessaly.

The burners 11', 12 can be supplied with different fuels, the fuel supplied to burner 11 containing constituents, from which the fuel supplied to burner 12 is free. The same fuel, containing constituents which are harmful for the second stage of higher temperature may, however, be used for both burners, in which case, however, in the second stage, substances must be added to the fuel before it enters the burner 12, or to the combustion products in the immediate vicinity of the point Where the combustion gases are produced, which prevent the formation of aggressive constituents in the furnace gases, or their deposition on the metal parts to be protected.

The heater unit shown in FIG. 2 has a combustion chamber 13 common to both stages, each stage being fired in its own combustion zone 14 and 15, respectively, with its own burner 11 and 12, respectively.

The heater unit shown in FIG. 3 consists of two independent heaters, each of which has its own burner, and the heater-tube systems 10, of which are connected together by a pipe-line 18, the two individual heaters being thereby connected together by a pipe-line 18, the two individual heaters being thereby connected in series.

What is claimed is:

1. A tubular heater for heating the gaseous working medium of a closed-cycle gas turbine plant comprising walls confining a first and a second chamber for the throughfiow of combustion gases, a tube system made of heat-resistant, austenitic alloy steels defining a flow path for the medium to be heated having two serially arranged parts, namely a first part and a second part through which the said medium flows after having passed through said first part; said first part of the tube system being arranged in said first chamber and said second part of the tube system being arranged in said second chamber, so that said second part is subjected to a higher temperature range than said first part; and means producing combustion gases of different type circulating through said chambers so as to impinge on said first and said second part, respectively, of the tube system; the combustion gases circulating through said second chamber being of the type which makes possible the formation of an oxide film which protects the heating tubes at said higher temperature range, and the combustion gases circulating through said first chamber being of the type which makes possible the formation of and oxide film which protects the heating tubes at the lower temperature range to which said first part of the tube system is subjected but which could adversely affect the formation of an oxide film protecting the heating tubes when subjected to said higher temperature range.

2. The combination defined in claim 1 in which the combustion gases circulating through the second chamber are those of a fuel giving combustion gases of the said type.

3. The combination defined in claim 1 in which the combustion gases circulating through the second chamber are those of a fuel giving combustion gases which could per se adversely affect the formation of an oxide film protecting the heating tubes at said higher temperature range, but which combustion gases contain additives which make possible the formation of an oxide film protecting the heating tubes.

References Cited by the Examiner UNITED STATES PATENTS JAMES W. WESTHAVER, Primary Examiner. 

1. A TUBULAR HEATER FOR HEATING THE GASEOUS WORKING MEDIUM OF A CLOSED-CYCLE GAS TURBINE PLANT COMPRISING WALLS CONFINING A FIRST AND SECOND CHAMBER FOR THE THROUGHFLOW OF COMBUSTION GASES, A TUBE SYSTEM MADE OF HEAT-RESISTANT, AUSTENITIC ALLOY STEELS DEFINING A FLOW PATH FOR THE MEDIUM TO BE HEATED HAVING TWO SERIALLY ARRANGED PARTS, NAMELY A FIRST PART AND A SECOND PART THROUGH WHICH THE SAID MEDIUM FLOWS AFTER HAVING PASSED THROUGH SAID FIRST PART; SAID FIRST PART OF THE TUBE SYSTEM BEING ARRANGED IN SAID FIRST CHAMBER AND SAID SECOND PART OF THE TUBE SYSTEM BEING ARRANGED IN SAID SECOND CHAMBER, SO THAT SAID SECOND PART IS SUBJECTED TO A HIGHER TEMPERATURE RANGE THAN SAID FIRST PART; AND MEANS PRODUCING COMBUSTION GASES OF DIFFERENT TYPE CIRCULATING THROUGH SAID CHAMBERS SO AS TO IMPINGE ON SAID FIRST AND SAID SECOND PART, RESPECTIVELY, OF THE TUBE SYSTEM; THE COMBUSTION GASES CIRCULATING THROUGH SAID SECOND CHAMBER BEING OF THE TYPE WHICH MAKES POSSIBLE THE FORMATION OF AN OXIDE FILM WHICH PROTECTS THE HEATING TUBES AT SAID HIGHER TEM- 